Condenser relaxation circuit



April 19, 1938.

o. SQPUCKLE 2,114,938

CONDENSER RELAXATION CIRCUIT Filed April 17, 1934 INVENI'OR OWEN s.PUICKLE w mw ATTORNEYS Patented Apr. 19, 1938 UNITED STATES PATENT()FICE CONDENSER RELAXATION CIRCUIT Britain Application April 17, 1934,Serial No. 721,053 In Great Britain May 5, 1933 6 Claims.

This invention relates to electrical time base circuits and systems forproducing waves of potential of the type known as condenser relaxationcircuits.

In circuits or systems of this type as usually arranged, a controllingcondenser is connected through an impedance to a source of continuousvoltage so as to be charged up at a rate regulated by the aforesaidimpedance, a discharging de- 10 vice connected directly across thecondenser being arranged to bring about a sudden discharging of thecondenser at intervals. In an alternative arrangement, the condenser,instead of being connected across the discharging device, is connectedacross the aforesaid impedance so that the condenser is discharged at arate regulated by the said impedance and suddenly charged at intervals.In both cases the condenser is alternately charged and discharged, thechange of charge in one direction being regulated so as to produce acontinuously varying potential having a desired characteristic whilstthe change of charge in the other direction is in the nature of a suddenrestoration of the state of charge on the condenser to a preset value.For convenience, the impedance which controls the rate of change ofcharge in one direction so as to produce a varying potential having adesired characteristic will be referred to in this specification as thecharging device, and the device by which the charge on the condenser issuddenly restored to a preset value at intervals will be referred to asthe discharging device, and it will be understood that in case thealternative arrangement described above is adopted, the charging devicemay have the effect of reducing the actual charge on the condenser andthe discharging device may have the effect of increasing the charge onthe condenser.

40 Circuits or systems of'the kind to which this invention relates areused in connection with electrical oscillographs for providing a timebase deflection. They are also used for controlling electrical scanningdevices in television systems.

45 In these applications, considerable difiiculty has the operationof agaseous discharge valve tends to v mionic valves.

' In the case where a very high frequency of operbe upset when it iscalled upon to discharge at varying time intervals as is required incertain applications to television systems.

The object of the present invention is to provide an improveddischarging system employing hard thermionic valves which will be moresatisfactory in operation and will be capable of discharging thecontrolling condenser more suddenly than the known arrangement describedabove. 10

According to a subsidiary feature of the invention, in order to enablethe anode circuit of the second valve to be supplied from the samesource of continuous voltage as is used for charging the regulatingcondenser, the cathode of the first 15 valve is connected to that poleof the regulating condenser to which the charging device is connected,the anode of the first valve being connected through the resistance inthe anode circuit of that valve to the positive pole of the source of 2continuous voltage. 0

The invention will be more particularly described with referenceto theaccompanying drawing in which:

Figure 1 is a circuit diagram showing the preferred arrangement forcarrying the invention into effect when used for controlling a cathoderay oscillograph employed for examining wave forms, Fig. l is afragmentary figure showing a modification of the arrangement shown inFig. 1, and

v Figure 2 illustrates another modification. 40

Referring now to this drawing, a circuit of the well known type forrectifyingalternating currents is shown on the left hand side while thedeflecting plates of a cathode ray oscillograph CRO are shown on theright hand side. The po-; tential on one of these oscillographdeflecting plates, viz. the plate Pr, is derived from a selected one ofthe controlling capacities C1, C2, C3 and C4.

ation is required however no condenser such as C1, C2, C3 or C4 needused, the stray capacities being relied on instead. The selectedcontrolling capacity is alternately charged and discharged ashereinafter described so as to cause the beam of cathode rays to executea traversing movement over the screen.

The capacity C1, C2, C3 or C4 is charged by means of a currentregulating device such as the pentode P1 which may be a screenedtetrode, which is connected in series with the capacity to be chargedand has a screen whose potential can be adjusted by means of thepotentiometer R4, the control grid being tied to the cathode, which isconnected to the negative pole of the supply. While this arrangement ispreferred it is to be understood that the control grid may be used inthe normal manner instead of the screen for adjusting the anode currentof the valve.

The discharging of the condenser is brought about by a triode T1assisted by the pentode P2 the former being connected through aresistance R1 across the condenser to be discharged and the latterhaving its anode connected to the grid of the triode T1. The controlgrid of the pentode P2 is connected to its cathode through a gridbiasing resistance R and the anode resistance R2 is so adjusted that thecontrol grid of the valve T1 is normally biased to a high negativevalue.

In the quiescent condition, which is of course not a lasting one, thatis to say with the controlling capacity discharged, the grid of thetriode T1 is very negative due to the large current flowing in the anodecircuit of the pentode P2. The controlling capacity, e. g. C1, thencharges, at a rate determined by the anode current of the valve P1,until the cathode of the triode T1 reaches a low enough potential topass anode current. The resulting change of voltage across theresistance R1 is communicated to the control grid of the pentode P2through a condenser C with the result that the control grid of P2becomes negative thus reducing the anode ourrent of P2 and making thegrid of the triode T1 more positive. The resulting further increase inthe anode current of T1 increases the fall of potential on the grid ofthe valve P2 so that the efiect is a cumulative one and the grid of 'T1rises rapidly to a positive value with respect to its cathode. The anodecurrent of the valve T1 therefore rapidly reaches a high value so that arapid discharge of the controlling capacity. is brought about. The timeconstant of the circuit CR is so chosen that the control grid of thepentode P2 remains negative up to almost the end of the discharge of thecontrolling capacity. When the controlling capacity is dischargedhowever, the anode potential of the triode T1 rises with the result thatthe grid of the pentode P2 is forced towards zero making the grid of thetriode T1 become very negative and thus resetting the circuit for thenext cycle of operations.

While the arrangement described above is preferred it is to beunderstood that, if desired, the arrangement may be reversed by alteringthe position of the condenser to be charged and discharged, e. g. C1, tothat shown at C in Fig. 1a, when the condenser will he suddenlycharged'by the two valve T1 and P2 and relatively slowly discharged bythe valve P1, and such an arrangement is intended to be included withinthe scope of the claims.

Included in the anode circuit of the triode T1 of this resistance therate of discharge of the trolling condenser. By the normal bias on thegrid of the'valve controlling capacity can be altered. The lower thevalue of the resistance R1 the greater will be the rate at which thecontrolling capacity is discharged. On the other hand, the higher thevalue of the resistance R1, the more rapidly will the 5 dischargingcurrent rise to its maximum value and the more suddenly will it be cutoff at the end of the discharging period. The resistance R2 should beadjusted to set the amplitude of the time base sweep.

The maximum value to which the anode current of the valve T1 risesduring the discharge of the controlling capacity, is limited by reasonof the fact that the flow of grid current in the valve T1 results in afall of potential across the resistance R2. Where it is desired toobtain 'a more rapid discharge of the controlling capacity than ispracticable with the arrangement illustrated in Figure 1, thearrangement illustrated in Figure 2 may be employed. arrangement, theplace of the resistance R2 is taken by a thermionic valve V whose anodeis connected to the positive voltage supply and whose cathode isconnected directly to the con- In this trol grid of T1 and through abiasing resistance Rv to the anode of the valve P2. The valve V has acontrol electrode connected directly to the anode of the pentode P2.

With this arrangement, during the charging of the controlling condenser,the anode current of of the valve P2 is reduced and acumulative rise ofpotential on the grid of the valve T1 occurs as has already beendescribed with reference ing to the arrangement of the valve V however,the reduction of the anode current of the valve P2 results in areduction of the fall of potential acrossthe resistance Rv andconsequently in a When a small rise of anode to Figure 1 of theaccompanying drawing. Ow-.-f%0

reduction of the impedance of the valve V. The; 4 .5

, rise of'potential on the grid of the valve'T1fis consequentlyaccelerated. 'In addition the limiting effect of grid current inthevalve T1 on the rate of discharge of the controlling capacity isminimizedo-wing to the reduced impedance of the valve V. The dischargingcurrent conse-- "quently rises to a higher maximum value than would bethe case if the impedance of the connection between the positivepotential point and the control grid of the valve T1 remained at itsznormal value during the discharging of the con- By adjusting theresistance V and therefore the normal impedance of this valve can bevaried. This results in a variationroo tapping on the potentiometer R4and the latterthus controls the anode current of the: pentode P1 andhence the speed of the time base sweep.

The wave to be examined is impressed across the terminals W1 and W2 ofwhich W1 is connected to the gun GN of the oscillograph whilst. .70

W2 may be connected to the deflector plate S of the oscillograph.

In the circuit arrangement shown, the wave to be examined is alsoemployed as a synchronizing signal for the time base sweep. For thispurpose-.75

a triode T2 is provided for amplifying the synchronizing signal receivedfrom W2. The grid of the triode T2 is connected to the point W2 via atapping on a potentiometer R3. The anode of the triode T2 is connectedto a resistance R5 and to'the screen of' the pentode P so that theresistance R5 and triode T2 form a two part potentiometer the impedanceof one side of which (viz. that formed by the triode T2) varies with theinstantaneous amplitude of the synchronizing wave derived from W2. Thereis thus applied to the screen of the pentode P2 9. synchronizing wavewhich may be an amplified or an attenuated copy of the wave to beexamined according to the adjustment of the potentiometer R3.

- This synchronizing wave takes controlof the discharge of thecontrolling capacity and causes this discharge to occur at the samepoint on the curve of the examined wave form on each occasion so thatthe individual traces are superposed. It will be understood that bysuitable adjustment of the resistance R2 the amplitude of the time basesweep may be set so that the frequency of the discharge becomes asub-multiple of the frequency of the synchronizing wave. Thus althoughwhen a synchronizing signal is employed the value of the resistance R2does not determine the exact amplitude of the time base sweep, itselects one from a number of possible amplitudes at which the dischargemight occur for any given frequency and amplitude of the synchronizingsignal.

The possibility of amplification of the synchronizing signal allowsperfect synchronization to be maintained even when the amplitude of theexamined wave form is very small. Since this amplification does notafiect the wave applied to the plate S of the oscillograph thepossibility of distortion due to the amplification necessary forsynchronization is avoided.

In the arrangement just described, the potentiometer R3 is fed with asmall amount of energy from the circuit being examined and a suitablepercentage of this is applied to the grid of the triode T2 therebyaltering its conductivity and altering the potential applied to thescreen of the pentode P2. While this arrangement is preferred it is tobe understood that the synchronizing signal'may if desired be applieddirectly to the control grid or screen of P2 instead of to the controlgrid of the triode T2. Alternatively it may be fed directly to the valveT1.

With the arrangement illustrated in Fig. 1 the positive crests of thewave to be examined produce a decrease in the impedance of the triode T2and consequently a decrease in the screen voltage of the pentode P2giving rise to an increase in the potential on the grid of the dischargetriode T1.

In order to permit of centering the image on the screen of theoscillograph two potentiometers Q1 and Q2 are connected across the H. T.supply, the tappings being connected to the appropriate deflectingplates (Pys, Pms). To enable the potentials on the plates to be madepositive or negative with respect to the gun GN the latter is itselfconnected to the junction of the two resistances Rs, R1.

Connected between the anode or gun GN of the oscillograph, and thesource of H. T. potential is a condenser C5 which has the effect ofproviding a low impedance path for the capacity current through theoscillograph during the fly-back or rapid return of the oscillographspot, the low impedance path having the effect of preventing the theaccompanying drawing can be employed with very little modification forproducing the scanning potentials to be applied to the oscillograph of acathode ray television system. For this purpose the system composed ofthe valves,T1, P2

may be arranged to discharge the controlling capacity when the potentialacross the latter reaches a preset limit, the valve T2 being replaced bya fixed resistance. Alternatively a synchronizing signal derived fromany suitable source -may beapplied to the grid of T2 or directly to .thecontrol grid or screen grid of P2 for the purpose of synchronizing thedischarge. In the case of a velocity modulated television system, thetelevision signal may be applied to the control grid or otherappropriate electrode of the.

valve P1 for the purpose of modulating the anode current of this valve.

I claim:

1. A relaxation oscillator comprising a condenser, a direct currentsource, and an impedance, one terminal of said condenser and oneterminal of said impedance each being connected to said direct currentsource and the other terminals of said condenser and impedance beingjoined, a hard thermionic valve having an anode, cathode and grid, asecond impedance, an anode circuit for said valve connected between thejunction of said condenser and the first said impedance and a point insaid direct current source having a different potential than the pointto which the first said impedance is connected, said anode circuitcomprising the space path of said valve together with said secondimpedance connected in series with and on the anode side of said spacepath, a third impedance, a second hard thermionic valve having an anode,cathode and grid and having its cathode connected to a point in saiddirect current source and its anode connected through said thirdimpedance to a point in said direct current source having a higherpotential than the point to which the cathode of said second valve isconnected, means for coupling the anode of said first valve to the gridof said second valve, and means for coupling the grid of said firstvalve to the anode circuit of said second valve.

2. A relaxation oscillator according to claim 1, in which the cathode ofthe first mentioned valve is connected to the junction of the saidcondenser and the first mentioned impedance, and the anode of the firstmentioned valve is connected through the impedance in the anode circuitof that valve to the positive pole of said source.

3. A device in accordance with claim 1 in which said third impedancecomprises a fourth impedance and a third valve having an anode cathodeand grid, the fourth impedance being connected between the anode of thesecond valve and the cathode of the third valve, the anode of the thirdvalve being connected to said higher potential point in the directcurrent source and there being a connection from the anode of the secondvalve to the grid of the third valve and a connection from the cathodeof the third valve to the grid of the first mentioned valve.

4. A relaxation oscillator according to claim 1 wherein the secondmentioned thermionic valve has a screen grid and wherein a synchronizingsignal is applied to said screen grid through a two-part potentiometerone. side of which consists of a thermionic valve whose impedance ismade to vary with the instantaneous amplitude of the synchronizing wave.

5. In an electrical time base circuit or wave producing system of thetype referred to, a controlling condenser, a direct current source forcharging said condenser, a charging impedance, said impedance and saidcondenser being connected in series across said source a hard thermionicvalve, a resistance, the anode of said valve being connected throughsaid resistance to the positive pole of the said source and its cathodeconnected to the junction of said charging impedance and said condenser,a second therrnionic valve having an anode, a cathode and grid, a secondresistance, said second valve having its cathode connected to thenegative pole of said source and its anode connected through said secondresistance to the positive pole of said source, a leak resistance,saidgrid for the second valve being connected through said leak resistancetoa point in said source, a connection between the anode of the secondvalve and the grid of the first valve. a direct current stoppingcondenser, and a connection through said direct current stoppingcondenser between the anode of the first valve and the controlling gridof the second valve, the time constant of the said stopping condenserand leak resistance so functioning that the control grid of the secondvalve remains negative until close to the end of the discharge of thecontrolling capacity.

,6. Anielectrical time base circuit as claimed in claim 5, wherein theresistance connected in the anode circuit of the second thermionic valveis adjustable for the purpose of adjusting the normal bias on the gridof the first valve to set the amplitude of the time base sweep.

OWEN STANDIDGE PUCKLE.

